-corresponding to a given binary package name, version, and architecture. If
-undef is passed as the architecture, returns a list of references to all
-possible pairs of source package names and versions for all architectures,
-with any duplicates removed.
+corresponding to a given binary package name, version, and architecture.
+
+If undef is passed as the architecture, returns a list of references
+to all possible pairs of source package names and versions for all
+architectures, with any duplicates removed.
+
+If the binary version is not passed either, returns a list of possible
+source package names for all architectures at all versions, with any
+duplicates removed.